The present invention relates to a fluid-operated torque wrench for and a method of tightening and loosening fasteners.
Power-driven torque tools require the use of reaction members. Reaction members usually abut against a stationary object, such as for example an adjacent nut, to stop the tool housing from turning backwards, while a fastener, such as for example a nut, turns forwards. The abutment force for the tool with a torque 10,000 ft. lb can be as high as 30,000 lb, which is applied as a side load to the adjacent nut in one direction and to the nut to be turned in the opposite direction. This enormous abutment force tries to bend the bolt and to increase the turning friction of the nut. On regular applications this is not a problem because the bolt is designed to take the side loads, and the torque recommendations by manufacturers of equipment usually take the side load into consideration.
The problem occurs during tightening up of critical applications when a scatter of a bolt load applied to all fasteners on a flange or a casing can not vary too much, or when loosening of corroded fasteners. The corrosion of a corroded fastener usually occurs between the engaging threads of the nut and the bolt. On hot applications, grease applied for assembly usually dries up and binds the threads together. When a high torque with a high side load is applied to such a nut, then merely a half of the threads between the bolt and the nut are engaged on one side and the threads on the engaged side start gripping. This causes the bolt thread to gall and requires more torque and thus more side load to take the nut off, which can totally ruin the bolt and the nut threads. Hot applications are usually critical. Since most of the bolts used on hot applications like turbines and casings are either stainless or precision manufactured, the replacement costs are extremely high.
The galling also occurs not just between the threads of the bolt and the nut, but also between the face of the nut and the face of the flange in which the fastener is introduced, since the side load changes a perpendicular position of the nut to be turned. This in turn increases the turning friction of the nut and makes the bolt load generated by the torque unpredictable which can result in leaks or joint failures.
Some of the tools provided with reaction members are disclosed, for example, in U.S. Pat. Nos. 3,361,218, 4,549,438, 4,538,484, 4,607,546, 4,619,160, 4,671,142, 4,706,526, 4,928,558, 5,027,932, 5,016,5, 5,142,951, 5,152,200, 5,301,574, 5,791,619, 6,260,443, and 6,715,381.